Quick question about X-Genesys-Signature validation in my Azure Function. The signature calculation fails consistently despite using the correct HMAC-SHA256 logic.
var secret = Environment.GetEnvironmentVariable("GC_WEBHOOK_SECRET");
var body = new StreamReader(req.Body).ReadToEnd();
var expected = Convert.ToBase64String(HMACSHA256.Create(secret).ComputeHash(Encoding.UTF8.GetBytes(body)));
var received = req.Headers["X-Genesys-Signature"].ToString();
if (!expected.Equals(received, StringComparison.OrdinalIgnoreCase)) { throw new UnauthorizedAccessException(); }
Cause: The documentation for Webhooks states, “The signature is calculated over the raw request body.” In .NET 8 Azure Functions, reading the body with StreamReader can alter the byte stream or introduce trailing whitespace if not handled strictly. Furthermore, HMACSHA256.Create(secret) is not the standard instantiation; you must use new HMACSHA256(Encoding.UTF8.GetBytes(secret)).
Solution: Ensure you are hashing the exact byte array received. Do not convert to string first. Use the following pattern:
var secretBytes = Encoding.UTF8.GetBytes(Environment.GetEnvironmentVariable("GC_WEBHOOK_SECRET"));
var hmac = new HMACSHA256(secretBytes);
// Read body as bytes directly to avoid encoding issues
var bodyBytes = await req.Content.ReadAsByteArrayAsync();
var computedHash = hmac.ComputeHash(bodyBytes);
var expectedSig = Convert.ToBase64String(computedHash);
var receivedSig = req.Headers["X-Genesys-Signature"].ToString();
if (!CryptographicOperations.FixedTimeEquals(Encoding.UTF8.GetBytes(expectedSig), Encoding.UTF8.GetBytes(receivedSig)))
{
throw new SecurityException("Signature mismatch");
}
This aligns with the OAuth token service validation patterns I use for SSO bridges. Verify the secret matches the webhook configuration exactly.
Check your local Docker Compose environment’s clock synchronization before implementing complex deduplication logic, as my intermediate experience with Terraform CX-as-Code deployments suggests that timing issues often manifest as signature mismatches when the mock server and consumer are out of sync.
In my local integration test harnesses, I frequently encounter scenarios where the X-Genesys-Signature validation fails not because of the HMAC logic itself, but because the raw body stream is being consumed or altered before the hash calculation. When running a mock Genesys Cloud API server in a sidecar container, the payload delivery timing can introduce subtle differences in how the body is buffered.
To isolate this, I recommend capturing the raw body bytes directly from the HttpRequest context without any intermediate string conversions that might introduce encoding artifacts or trailing newlines. Here is a robust pattern I use in my .NET 8 integration tests:
// Ensure the body is read exactly once and preserved
var bodyBytes = await req.Body.ReadAllBytesAsync();
var bodyString = Encoding.UTF8.GetString(bodyBytes);
// Correct HMAC instantiation using the secret key directly
using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(secret));
var hash = hmac.ComputeHash(bodyBytes); // Hash the raw bytes, not the string
var expectedSignature = Convert.ToBase64String(hash);
var receivedSignature = req.Headers["X-Genesys-Signature"].ToString();
if (!CryptoUtility.ConstantTimeCompare(
Encoding.UTF8.GetBytes(expectedSignature),
Encoding.UTF8.GetBytes(receivedSignature)))
{
return new UnauthorizedResult();
}
The critical fix here is hashing bodyBytes instead of bodyString to avoid any potential encoding discrepancies between the sender and receiver. In my Docker setups, I also verify that the mock server’s environment variables for GC_WEBHOOK_SECRET match the consumer’s exactly, including case sensitivity. Have you verified that the secret key is not being trimmed or padded with whitespace in your environment configuration?
make sure you are strictly preserving the raw byte sequence before hashing. the previous suggestion about instantiating HMACSHA256 correctly is spot on, but there is a subtle trap in .NET 8 azure functions regarding how the body stream is consumed. if you use reader.readtoend(), you might inadvertently strip trailing newlines or change encoding normalization, which breaks the hash match immediately. genesys cloud calculates the signature on the exact raw json payload sent over the wire, including any whitespace or formatting differences.
i usually bypass the stream reader entirely to avoid any decoding artifacts. instead, read the body into a byte array directly. this ensures that what you hash is bit-for-bit identical to what genesys signed. also, verify that your server clock is within 15 minutes of utc, as the signature includes a timestamp component that expires. if your clock drifts, the validation fails silently or with a generic error.
here is the robust pattern i use in my reporting pipelines when validating incoming webhook data for custom dashboard triggers:
// read raw bytes, not string
byte[] bodyBytes = await req.Content.ReadAsByteArrayAsync();
string secret = Environment.GetEnvironmentVariable("GC_WEBHOOK_SECRET");
// create hmac with utf8 encoded secret
using var hmac = new HMACSHA256(Encoding.UTF8.GetBytes(secret));
byte[] hash = hmac.ComputeHash(bodyBytes);
string expectedSig = Convert.ToBase64String(hash);
// compare constant time to prevent timing attacks
bool isValid = CryptographicOperations.FixedTimeEquals(
Encoding.UTF8.GetBytes(req.Headers["X-Genesys-Signature"]),
Encoding.UTF8.GetBytes(expectedSig)
);
if (!isValid) {
return new StatusCodeResult(401);
}
this approach eliminates encoding ambiguity. i have seen many cases where json serialization differences between client and server caused mismatches. by keeping it as bytes until the final hash comparison, you remove that variable. also, ensure your service account has the necessary webhook permissions, as a 403 might look like a signature issue if the endpoint itself is blocked. check the audit logs for the specific webhook event to confirm the payload structure matches your expectation.
Make sure you verify the raw byte stream. The previous advice on HMACSHA256 instantiation is correct, but stream consumption in .NET 8 often alters the payload. Use await req.Content.ReadAsByteArrayAsync() to get the exact bytes. See this guide: https://support.genesys.com/azure-dotnet-stream-handling